Sx-nickel alloy having improved tmf properties, raw material, and component

ABSTRACT

Provided is a composition of a nickel-based superalloy with Ni-8Cr-10Co-0.6Mo-8Ta-8W-1.25Re-5.7Al-0Ti-0.1Hf-0.25Si-0.008B-0.0210C-0.02Y, by which composition improved TMF properties are achieved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application No. PCT/EP2017/069917, having a filing date of Aug. 7, 2017, based on European Application No. 16185120.9, having a filing date of Aug. 22, 2016, the entire contents both of which are hereby incorporated by reference.

FIELD OF TECHNOLOGY

The following relates to a nickel-based SX alloy having improved TMF properties, a raw material and a component.

BACKGROUND

To make a higher turbine entry temperature and thus a higher efficiency possible, SX materials based on nickel are being examined at present. These materials are said to have a significantly higher creep resistance compared to known SX materials and, particularly at high temperatures, have a significantly increased tensile strength. However, first investigations on the TMF behavior show that the materials can tend to have brittle behavior and thus a reduced TMF life at relatively low temperatures (373 K) and high expansion swing ranges.

The LCF life at high expansion swing ranges is likewise reduced by the brittle fracture behavior between room temperature and 923 K.

Although the creep properties were previously considered to be life-determining, the TMF properties are increasingly gaining in importance. This is due to improved cooling air concepts which result in local cold and hot regions: at the same time, the time intervals of steady-state use are becoming increasingly short. The systematic investigation of TMF properties is still in its infancy. For this reason, the problems associated with this material have hitherto not become known.

SUMMARY

The description presents only working examples of embodiments of the invention.

A material having the following composition is advantageous:

Nickel-based alloy comprising at least (in % by weight):

Chromium (Cr) 7.0%-9.0%, in particular 8.0% Cobalt (Co) 9.0%-11%,  in particular 10%, Molybdenum (Mo) 0.4%-0.8%, in particular 0.6%, Tantalum (Ta) 7.0%-9.0%, in particular 8.0%, Tungsten (W) 7.0%-9.0%, in particular 8.0%, Rhenium (Re)  1.0%-1.30%, in particular 1.25%, Aluminum (Al) 5.0%-6.4%, in particular 5.7%, Hafnium (Hf) 0.08%-0.12%, in particular 0.1%, Silicon (Si) 0.018%-0.32%,  in particular 0.25%, Boron (B) 0.003%-0.015%, in particular 0.008%, Carbon (C) 0.01%-0.05%, in particular 0.0210%, Yttrium (Y) 0.017%-0.023%, in particular 0.02%.

This material differs from previous Ni-SX compositions by a significantly higher proportion of chromium (Cr), a reduced proportion of rhenium (Re), the addition of silicon (Si) and yttrium (Y) and also in that it does not contain any titanium (Ti) except for impurities of not more than 0.1% by weight. The material also does not contain any Zirconium (Zi).

The material can consist or consist essentially of a nickel alloy which is Ni-8Cr-10Co-0.6Mo-8Ta-8W-1.25Re-5.7Al-0Ti-0.1Hf-0.25Si-0.008B-0.0210C-0.02Y.

The new material has the following advantages:

The addition of silicon (Si) increases the TMF strength by a factor of 2. This effect is due to the following actions of silicon:

-   -   silicon (Si) increases the oxidation resistance,     -   addition of silicon (Si) results in an increased yield stress at         low temperatures, which in the TMF test leads to reduced         compressive stresses in the high-temperature range under         out-of-phase conditions and thus to a lower risk of         recrystallization.

The LCF life is increased by the increased yield stress at low temperatures and high expansion swing ranges. Due to the reduction in the proportion of rhenium (Re), the risk of formation of TCP phases, which have a very negative effect on the TMF behavior if they are formed during operation, is decreased.

In combination with the removal of titanium (Ti), the reduction in the amount of rhenium (Re) also makes it possible to increase the proportion of chromium without stabilizing undesirable TCP phases. This should give the new material oxidation properties which are at least at the level of the alloy 247.

The addition of yttrium (Y) here results in the material having particularly good cyclic oxidation properties (improvement in the Al₂O₃ covering layer adhesion).

In the titanium-free alloy, the silicon (Si) is predominantly incorporated into the γ′ phase, while in the case of titanium-containing materials it is incorporated into the γ phase. The enrichment of the γ phase with silicon (Si) is rather undesirable since this would promote the precipitation of brittle phases in the channels (e.g. G phase). Furthermore, the shear strength of the γ′ phase is increased by the incorporation of silicon into this phase.

The reduced proportion of rhenium (Re) makes the alloy significantly more advantageous. The γ′ proportion changes only insignificantly.

The creep resistance accordingly remains virtually uninfluenced.

The alloy described above is completely novel. If the TMF life can actually be increased by a factor of 2, the following advantages result:

-   -   increase in life of the turbine blades,     -   decreased LCCs resulting therefrom,     -   technological leadership provided by proprietary SX alloy.

Although the invention has been illustrated and described in greater detail with reference to the preferred exemplary embodiment, the invention is not limited to the examples disclosed, and further variations can be inferred by a person skilled in the art, without departing from the scope of protection of the invention.

For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. 

1. A nickel-based alloy comprising at least (in % by weight): Chromium (Cr) 7.0%-9.0%, Cobalt (Co) 9.0%-11%,  Molybdenum (Mo) 0.4%-0.8%, Tantalum (Ta) 7.0%-9.0%, Tungsten (W) 7.0%-9.0%, Rhenium (Re)  1.0%-1.30%, Aluminum (Al) 5.0%-6.4%, Hafnium (Hf) 0.08%-0.12%, Silicon (Si) 0.018%-0.32%,  Boron (B) 0.003%-0.015%, Carbon (C) 0.01%-0.05%, Yttrium (Y) 0.017%-0.023%


2. A powder, comprising at least an alloy as claimed in claim
 1. 3. A component comprising at least an alloy as claimed in claim 2 or produced from a raw material.
 4. The component as claimed in claim 3 which is a turbine blade.
 5. The alloy, raw material or component as claimed in claim 1, which does not comprise any titanium.
 6. The alloy as claimed in claim 1, which does not comprise any zirconium.
 7. The alloy of claim 1, wherein the nickel alloy is Ni-8Cr-10Co-0.6Mo-8Ta-8W-1.25Re-5.7Al-0Ti-0.1Hf-0.25Si-0.008B-0.0210C-0.02Y.
 8. A nickel-based alloy at least one of consisting essentially of and consisting of (in % by weight): Chromium (Cr) 7.0%-9.0%, Cobalt (Co) 9.0%-11%,  Molybdenum (Mo) 0.4%-0.8%, Tantalum (Ta) 7.0%-9.0%, Tungsten (W) 7.0%-9.0%, Rhenium (Re)  1.0%-1.30%, Aluminum (Al) 5.0%-6.4%, Hafnium (Hf) 0.08%-0.12%, Silicon (Si) 0.018%-0.32%,  Boron (B) 0.003%-0.015%, Carbon (C) 0.01%-0.05%, Yttrium (Y) 0.017%-0.023%.


9. The alloy of claim 1, wherein the nickel alloy consists of Ni-8Cr-8W-10Co-0.6Mo-8Ta-1.25Re-5.7Al-0Ti-0.1Hf-0.25Si-0.008B-0.0210C-0.02Y. 